1. Field of the Invention
The present invention relates to disc brakes and more particularly to improvements in large area contact disc brakes for vehicles.
2. Description of the Prior Art
The concept of the full annular disc brake is proposed for automobiles and light trucks and the present invention relates to an improvement over the structure of a full annular disc brake for such vehicles as described in PCT published application WO98/29671 published Jul. 9, 1999 in the name of Yvon Rancourt. Disc brakes for full annular disc brakes for larger vehicles such as trucks are described in U.S. Pat. No. 5,330,034 issued Jul. 19, 1994 and U.S. RE 35055 issued Oct. 10, 1995.
There are obvious advantages in having a complete annular array of friction pads contacting an annular disc on both sides of the disc. The braking or thermal energy distribution is related directly to the thermal resistance associated with both sides of the interface where the heat is generated. In a full annular brake there is a large area to distribute the braking energy more efficiently.
It has also been found that vibrations between the inner and outer pads are the major causes for brake squeal.
In a brake system, dynamic loading produces stresses and strains, the magnitude and distribution of which will depend not only on the usual parameters encountered previously but also on the velocity of propagation of the strain waves through the material of which the system is composed. This latter consideration, although very important when loads are applied with high velocities, may often be neglected when the velocity of application of the load is low. Since dynamic loading is conveniently considered to be the transfer of energy from one system to another, the concept of configuration (strain energy) as an index of resistance to failure is important. One of the important concepts is that the energy-absorbing capacity of a member, that is, the resistance to failure is a function of the volume of material available, in contrast to the resistance to failure under static loading, which is a function of cross-sectional area or section modulus.
One of the main problems in adapting the technology of a full annular brake system of the type described in the above mentioned patents is the consideration of weight and cost. It would be unrealistic, no matter what the advantages, to assume that a new full annular brake system would be accepted on the market at a price substantially higher than present day disc brakes. Furthermore any increase of weight compromises the fuel consumption.
It is an aim of the present invention to provide a brake system, especially for automobiles, that has improved heat distribution properties, and reduces the occurrence of wear.
It is still a further aim of the present invention to provide an annular disc brake system where the maximum brake performance is obtained.
A construction in accordance with the present invention comprises a disc brake assembly for a vehicle wheel wherein the wheel includes a hub journaled to an axle on the vehicle, the disc brake assembly comprises a housing mounted to the vehicle and at least an annular rotor disc within the housing and means mounting the rotor disc to the wheel which comprises an annular hub portion, the rotor disc further including an annular peripheral portion and at least a first radial planar friction surface on the annular peripheral portion; the housing includes a first annular brake shoe provided adjacent the first planar friction surface of the disc and movable axially towards and away from the first friction surface; and the rotor comprising an annular array of axially extending cooling fins integral with the rotor between the hub portion and the peripheral portion.
In a more specific embodiment of the present invention the radial disc is provided with a second planar friction surface parallel to the first surface and the cooling fins are provided adjacent the first and second friction surfaces respectively.
In a still more specific embodiment of the present invention, the cooling fins have different radially and axially extending configurations in order to promote airflow turbulence and therefore enhance the heat dissipation characteristics of the rotor.